This application relates generally to electrochemiluminescent reactions, and more particularly to detecting the presence of an analyte of interest, and if desired quantitating the amount present, by measurement of electromagnetic radiation emitted by the system being investigated.
In Noffsinger, J. B. et al., Anal. Chem. 1987, 59, 865, experiments relating to chemiluminescence obtained utilizing a reaction sequence involving amines and a ruthenium-containing luminophore (Ru(bpy)33+) (xe2x80x9cbpyxe2x80x9d shall in all instances herein stand for xe2x80x9cbipyridylxe2x80x9d) were disclosed. See, also, Lytle, F. E. et al., Photochem. Photobiol. 1971, 13, 123. In this work, luminescence is achieved solely through chemical reactions, without triggering by electrochemical energy. While chemiluminescent techniques can be useful, electrochemiluminescent (xe2x80x9cECLxe2x80x9d) operations are preferable in several respects, for example: (1) there is greater control over the reaction sequence since the motive electrochemical energy can be interrupted with concomitant interruption of the reaction, whereas in chemiluminescent systems, the reaction sequence, once initiated, does not stop until completion; (2) luminophores can participate in multiple emissions whereas in chemiluminescent systems the luminophore only emits light once; (3) the apparatus employed is different from, and easier to work with than, that used in chemiluminescent techniques. However, successful generation of chemiluminescence with a particular system does not mean that the reaction system can be made to electrochemiluminesce, and thus the disclosure of Noffsinger et al. cannot fairly be extrapolated to predict similar results in an electrochemically stimulated system.
Early ECL reactions involved the annihilation of oppositely charged radical ions, produced by sequential oxidation and reduction at an electrode using a double potential step, for example, as described in Faulkner, L. R., et al., Electroanalytical Chemistry, A. J. Bard (Ed.), Vol. 10, Marcel Dekker, N. Y., 1977, Ch. 1; Tokel-Takvoryan, N. E., et al., Chem. Phys. Lett., 1974, 25, 235; Velasco, J. C., et al., Inorg. Chem. 1983, 22, 822; Luong, J. C., et al., J. Am. Chem. Soc. 1978, 100, 5790; Abruna, H. D., J. Electrochem. Soc. 1985, 132, 842; and Abruna, H. D., J. Electroanal. Chem. 1984, 175, 321. Upon homogeneous electron transfer between the sufficiently energetic and oppositely charged radicals, an excited state of one of the precursors can be formed, and subsequent emission by the species in the excited state occurs. Additionally, so-called energy deficient mechanisms involving triplet-triplet annihilations have been reported. See Freed, D. et al., J. Am. Chem. Soc. 1971, 93, 2097; Wallace, W. L. et al., J. Electrochem. Soc. 1978, 125, 1430.
In certain other ECL reactions, a luminophore has been used with an organic acid, such as an oxalate or pyruvate, to achieve electrogenerated chemiluminescence. Oxidative-reduction mechanisms, such as this, involve oxidation of Ru(bpy)32+ (herein, xe2x80x9cbpyxe2x80x9d stands for xe2x80x9cbipyridylxe2x80x9d) and the organic acid. However, in certain situations systems of this nature are disadvantageous because the reaction leading to luminescence is conducted at a pH which is disadvantageously acidic. These systems are lacking in versatility, since their application to assaying of numerous biological interactions requires a departure from physiological solution conditions, such as pH, leading to a disruption of the immunochemistry of the assayed system. Illustratively, see Ege, D. et al., J. Anal. Chem. 1984, 56, 2413; Rubinstein, I. et al., J. Em. Chem. Soc. 1981, 103, 512; Chan, M. M. et al., J. Am. Chem. Soc. 1979, 99, 5399.
In certain articles by Pragst and co-workers, a fluorescent aromatic hydrocarbon, oxazole or oxadiazole has been subjected to electrochemical energy in the presence of imidazole or pyridine derivatives in order to achieve luminescence. See Ludvik, J. et al., J. Electroanal. Chem. 1986, 215, 179; Pragst, F. et al., J. Electroanal. Chem. 1986, 197, 245; Pragst, F. et al., J. Electroanal. Chem. 1981, 119, 301; and Pragst, F. et al., J. Electroanal. Chem. 1980, 112, 339. However, in each of these instances the luminophore was not a metal-containing substance, but rather was a non-metallic organic compound.
Provision of materials and methods for conducting ECL reactions utilizing metal-containing ECL moieties and amine reductants, to exploit the combined benefits of both while avoiding the disadvantages attendant upon the use of each in other systems, would be a significant technological advance.
It is an object of the present invention to provide materials and methods suitable for generating electrochemiluminescence.
It is another object of the present invention to provide materials and methods suitable for the conducting of ECL assays.
It is a further object of the present invention to provide methods and materials suitable for the detection of electrochemiluminescence, and thereby a wide variety of analytes of interest which may be present over a wide range of concentrations.
It is an additional object of the present invention to provide methods and materials which are suitable for conducting highly sensitive ECL assays for the detection and quantitation of very small concentrations of analytes of interest.
It is still another object of the present invention to provide materials and methods suitable for conducting precise, repeatable, highly sensitive ECL detection and/or quantitation of analytes present over a wide concentration range in aqueous environments, as well as organic environments.
It is yet another object of the present invention to provide materials and methods suitable for an ECL assay to detect and/or quantitate metal-containing ECL moiety.
It is still a further object of the present invention to provide methods and materials suitable for ECL detection and quantitation assays of an analyte of interest at a pH which does not disrupt the immunochemistry of an assayed system, and which are particularly suitable for detection and quantitation of an analyte of interest at a physiological pH.
These and other objects of the present invention will become even more readily apparent after consideration of the following description of the invention.
As will be seen from the discussion hereinafter, the present invention is a powerful tool which permits attainment of the objects set forth in the preceding section.
Thus, in one aspect the present invention is a composition suitable for use in an ECL assay, wherein electromagnetic radiation emitted by said composition is detected, which composition comprises
(a) a metal-containing ECL moiety capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the excited ECL moiety to conditions sufficient to induce said emission;
(b) an amine or amine moiety which when oxidized forms a strong reducing agent; and
(c) an electrolyte capable of functioning as a medium in which the ECL moiety and amine or amine moiety can be oxidized.
In another aspect, the invention relates to a reagent suitable for use in providing a composition for conducting an ECL assay wherein electromagnetic radiation is emitted by a composition comprising members selected from the group consisting of (i) a metal-containing ECL moiety capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the excited ECL moiety to conditions sufficient to induce said emission, (ii) an amine or an amine moiety which when oxidized forms a strong reducing agent, and (iii) an electrolyte capable of functioning as a medium in which said ECL moiety and said amine or amine moiety can be oxidized, said reagent comprising an amine or amine moiety and one of the other two members of said group.
In a further aspect, the present invention is directed to a kit for performing an ECL assay wherein electromagnetic radiation emitted by a composition is detected, which kit contains (i) a metal-containing ECL moiety capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the excited ECL moiety to conditions sufficient to induce said emission, (ii) an amine or an amine moiety which when oxidized forms a strong reducing agent, and (iii) an electrolyte capable of functioning as a medium in which said ECL moiety and said amine or amine moiety can be oxidized, said kit comprising at least one separate component in which one or more members of the croup consisting of said ECL moiety (i), amine or amine moiety (ii), and electrolyte (iii) is included.
In still another aspect, the present invention relates to a method of generating emission of electromagnetic radiation, which comprises the steps of
(a) forming a composition comprising (i) a metal-containing ECL moiety capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the excited ECL moiety to conditions sufficient to induce said emission; (ii) an amine or amine moiety which, when oxidized, forms a strong reducing agent; and (iii) an electrolyte capable of functioning as a medium in which said ECL moiety and said amine or amine moiety can be oxidized;
(b) exposing the composition under suitable conditions to an amount of electrochemical energy effective to induce the composition to emit electromagnetic radiation; and
(c) detecting emitted electromagnetic radiation.
In an additional aspect, the invention also is directed to a method of detecting or quantitating an analyte of interest by ECL assay, which comprises
(1) forming a composition comprising
(a) a sample to be tested for the analyte of interest,
(b) at least one substance selected from the group consisting of
(i) additional analyte of interest or an analog of the analyte of interest,
(ii) a binding partner of the analyte of interest or its said analog, and
(iii) a reactive component capable of binding with (i) or (ii),
(c) a metal-containing ECL moiety capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the excited ECL moiety to conditions sufficient to induce said emission, said ECL moiety being capable of entering into a binding interaction with the analyte of interest or a substance defined in (b) (i), (b) (ii), or (b) (iii);
(d) an amine or an amine moiety which, when oxidized, forms a strong reducing agent, and
(e) an electrolyte capable of functioning as a medium in which said ECL moiety and said species can be oxidized;
(2) exposing said composition to an amount of electrochemical energy effective to induce the composition to emit electromagnetic radiation; and
(3) detecting emitted electromagnetic radiation.
In yet another aspect, the present invention relates to a system for ECL detection or quantitation of an analyte of interest in a sample, said system comprising:
(a) a sample,
(b) at least one substance selected from the group consisting of
(i) added analyte of interest or an analog of the analyte of interest,
(ii) a binding partner of the analyte of interest or its said analog, and
(iii) a reactive component capable of binding with (i) or (ii), wherein one of said substances is linked, either directly or through one or more other molecules, to a metal-containing ECL moiety which is capable of being converted to an excited state from which electromagnetic radiation is emitted upon exposure of the ECL moiety to conditions sufficient to induce said emission
(c) an amine or amine moiety which is capable of being converted to a strong reducing agent and an electrolyte;
(d) means for inducing the ECL moiety to emit electromagnetic radiation; and
(e) means for measuring the emitted radiation to determine the presence or quantity of the analyte of interest in the sample.
The xe2x80x9cECL moietyxe2x80x9d or xe2x80x9cmetal-containing ECL moietyxe2x80x9d is sometimes referred to as a xe2x80x9clabelxe2x80x9d, xe2x80x9clabel compoundxe2x80x9d, xe2x80x9clabel substancexe2x80x9d, etc. It is within the scope of the invention for the species termed xe2x80x9cECL moietyxe2x80x9d, xe2x80x9cmetal-containing ECL moietyxe2x80x9d, xe2x80x9corganometallicxe2x80x9d, xe2x80x9cmetal chelatexe2x80x9d, xe2x80x9ctransition metal chelatexe2x80x9d and xe2x80x9crare earth metal chelatexe2x80x9dxe2x80x94when utilized in certain of the composition, reagent, kit, method, or system embodiments in accordance with the inventionxe2x80x94to be linked to other molecules such as an analyte or an analog thereof, a binding partner of the analyte or an analog thereof, a further binding partner of such aforementioned binding partner, or a reactive component capable of binding with the analyte, an analog thereof or a binding partner as mentioned above. The above-mentioned species can also be linked to a combination of one or more binding partners and/or one or more reactive components. Additionally, the aforementioned species can also be linked to an analyte or its analog bound to a binding partner, a reactive component, or a combination of one or more binding partners and/or one or more reactive components. It is also within the scope of the invention for a plurality of the aforementioned species to be bound directly, or through other molecules as discussed above, to an analyte or its analog.
It is similarly within the scope of the invention for the aforementioned xe2x80x9ccompositionxe2x80x9d, hereinafter sometimes an xe2x80x9cECL compositionxe2x80x9d, or a xe2x80x9csystemxe2x80x9d to contain unstable, metastable and other intermediate species formed in the course of the ECL reaction, such as an ECL moiety in an excited state as aforesaid and the above-mentioned strong reducing agent.
Additionally, although the emission of visible light is an advantageous feature of certain embodiments of the invention it is within the scope of the invention for the composition (hereinafter sometimes xe2x80x9cECL compositionxe2x80x9d) or system to emit other types of electromagnetic radiation, such as infrared or ultraviolet light, X-rays, microwaves, etc. Use of the terms xe2x80x9celectrochemiluminescencexe2x80x9d, xe2x80x9celectrochemiluminescentxe2x80x9d, xe2x80x9celectrochemiluminescexe2x80x9d, xe2x80x9cluminescencexe2x80x9d, xe2x80x9cluminescentxe2x80x9d and xe2x80x9cluminescexe2x80x9d in connection with the present invention does not require that the emission be light, but admits of the emission""s being such other forms of electromagnetic radiation.
Substantial advantages are conferred on the practitioner of the present invention. The materials and methods in accordance with the invention provide an elegant technology for conducting the ECL detection and quantitation of an analyte of interest over a wide concentration range, down to a very small analyte concentration, in aqueous as well as organic environments. Good precision, and repeatability of detection and auantitation measurements are obtained. The utilization of metal-containing ECL moieties, especially metal chelates, in combination with amine-derived reductants, permits the practitioner of the invention to obtain advantages associated with use of each of these components, while avoiding disadvantages commonly encountered with other ECL techniques involving one or the other, but not both. Thus, the control over the reaction and the convenience of operation attendant upon using metal-containing species can be obtained without sacrifice of the capability of operation at a physiological pH. Conversely, the use of amine-derived reductants in the ECL interaction is advantageous: detection and quantitation functions can be performed without disrupting the immunochemistry of highly interesting biological systems which exist at physiological pH, but those functions do not involve use of organic luminophores that are incompatible with the aqueous environments of many of the highly interesting biological systems.
Furthermore, the present invention is useful in the detection and quantitation of numerous and highly varied analytes of interest as is discussed in the further description of the invention which follows.
Additionally, the versatility of the present invention is evident from the fact that it is not only useful in conducting heterogeneous assays, but also homogeneous assays. In this connection, heterogeneous assays are those in which ECL moiety linked directly or through one or more other molecules to the analyte of interest or its analog is separated, prior to exposure of such ECL moiety to electrochemical energy from ECL moiety not linked to the analyte or its analog. Homogeneous assays, by way of contrast, are those in which there is no such separation before exposing the materials to electrochemical energy together. In the homogeneous assays of the present invention, electromagnetic radiation emitted when the ECL moiety is linked to the analyte or its analog differs from electromagnetic radiation emitted when the ECL moiety is not linked to the analyte or its analog. This can be achieved, for example, by sensing an increased or decreased emission amount corresponding to the presence of ECL moiety linked to analyte or its analog.